Copper base alloys



Patented Aug. 6, 1946 COPPER BASE ALLOYS John Sykes, Enfield, England, assignor to Enfield Rolling Mills Limited, Enfield, England, a company of Great Britain No Drawing. Application July 19, 1944, Serial No. 545,719. In Great Britain August 26, 1943 2 Claims.

This invention relates primarily to a method of producing a heat-treatable copper-base alloy particularly adapted for use in the manufacture of electrical contacts, resistance welding electrodes and other component parts of electrical apparatus where high electrical conductivity in combination with high strength and resistance to wear at both normal and elevated Working temperatures, are required. The invention also relates to the composition of a heat-treatable copper-base alloy.

The improved method according to the invention consists in adding chromium or a chromiumcopper master alloy to a copper melt so that chromium is present in the final alloy to the extent of from 0.4% to 1.0% and adding zinc and sulphur so as to be present in the final alloy to the extent of from 0.15% to 0.25% and from 0.05% to 0.5% respectively.

The improved alloy according to this invention consists of from 0.4% to 1% chromium, from 0.15% to 0.25% zinc, from 0.05% to 0.5% sulphur and balance copper.

In carrying out the improved method the use of a chromium-copper master alloy is to be preferred, and the zinc, which serves primarily to remove chromic oxide, is usually added before the sulphur in order to minimise reaction between these two elements.

It is to be understood that traces of impurities normal in commercial coppers may also be present.

Alloying is preferably carried out in an inert atmosphere, for example, the nitrogen atmosphere of a direct or indirect arc furnace, to avoid excessive oxidation of chromium, since such oxides have adverse eifects on the final product.

It is also desirable, though not essential, to cast by pouring with a nitrogen seal over the mould, usually with the aid of a hood disposed over a pouring funnel, nitrogen being circulated in the hood.

By subjecting the alloy to a two-stage heattreatment, hardness of the order of 100420 V. P. H. may be obtained, coupled with high eleccopper base alloy which comprises adding chrotrical conductivity and tensile strength. Further increase in hardness to as high as 150 V. P. H., together with improved tensile strength, may be achieved by subsequent cold working e. g. by cold drawing, cold forging or upsetting.

As an example of a suitable two-stage heat treatment for a 1 /8-in. diameter rod, the alloy material is heated to a temperature of between 900 C. and 1000 C. for hour, thereafter quenched and subsequently heated to a temperature of between 350 C. and 550 C. for 3 hours. The heating times are increased or decreased with variations in the mass of metal being treated.

Alternatively the alloy may be heated to'between 900 C. and 1000 C., extruded, air cooled and subsequently re-heated to between 350 C. and 550 C. for 2 hours or longer, again according to the mass of material being treated.

A sample of the improved alloy according to the invention, of composition: 0.62% chromium, 0.18% zinc, 0.17% sulphur and balance copper, after two-stage heat treatment, has been found to exhibit the following properties:

Yield Ultimate ten- Elongation Electricalconpoint sile strength on 2 in. ductivity Hardness Tons per Tons per sq. in. sq. in. Percent I. A. 0'. S V. P. H.

I claim:

1. The method of producing a heat treatable mium to a copper melt so that chromium is present in the final alloy to the extent of from 0.4% to 1% and adding zinc and sulphur so as to be present in the final alloy to the extent of from 0.15% to 0.25% and from 0.05% to 0.5% respectively.

2. A heat treatable copper base alloy consisting of from 0.4% to 1% chromium, from 0.15% to 0.25% zinc, from 0.05% to 0.5% sulphur and the balance copper.

JOHN SYKES. 

